What's happening to my back...?

I can't stand it I feel like my posture is getting really bad, I looked and my neck is loosing slouching forward from my back. It seems like this happened in a matter of a couple weeks. How do I get my posture COMPLETELY back, it's driving me nuts...I don't like the way it feels AT all.....Did this ever happen to you? How can I get rid of it? And does anyone know how to do that gymnastics thing where you arch your back until you can see your legs? Please help, the last question isn't that necessary...